1. Field of the Invention
The present invention relates to a magneto-resistance effect element which is configured such that a current is flowed in the direction perpendicular to the film surface thereof. The present invention also relates to a magnetic head and a magnetic recording/reproducing device which utilize the magneto-resistance effect element according to the present invention.
2. Description of the Related Art
As of now, a spin valve film (SV film) is widely available as a reproducing head for a hard disk drive (HDD). In this case, the reproduction is realized by utilizing Giant Magneto-resistive Effect (GMR) of the SV film and the biasing current is flowed parallel to the film surface of the SV film so as to constitute the SV film as a CIP (Current In-plane)-GMR film. The CIP-GMR film is made of a three-layered structure of a fixed magnetization layer of which the magnetization is fixed in one direction as reference, a free magnetization layer of which the magnetization is changed in accordance with an external magnetic field and a spacer layer disposed between the fixed magnetization layer and the free magnetization layer.
The free magnetization layer and the fixed magnetization layer are made of magnetic material such as Co, Ni, Fe and the spacer layer is made of non-magnetic conductor such as Cu, Ag, Au. Recently, there production is realized by utilizing Tunneling Magneto-resistive Effect (TMR) of the SV film and the biasing current is flowed perpendicular to the film surface of the SV film so as to constitute the SV film as a CPP (Current Perpendicular to plane)-TMR film. The CPP-TMR film is being mass-manufactured. Moreover, attention is paid to a CPP-GMR film in view of high density recording (Reference 1).
[Reference 1] IEEE Trans. Magn., Vol. 38, pp. 2277-, 2002
As described in Reference 1, it is required that the CPP-GMR film has an MR ratio (Magneto Resistive Ratio=resistance variation resistance) of at least about 3% in the HDD. In view of the enhancement of S/N, it is desired that CPP-GMR film has the MR ratio of 7% about twice as large as the required one of 3%. In the conventional CPP film, however, the MR ratio is within a range of 0.5 to 1.0% not to satisfy the above-described requirement. In this point of view, metal holes are formed in the spacer layer of the SV film to form the current-confined structure in the spacer layer in order to develop the MR ratio, that is, the S/N (Reference 2).
[Reference 2] JP-A 2006-54257 (KOKAI)
In Reference 2, the reproducing head has an MR ratio of 7.5% and a resistance area product (RA) of 0.6 Ωμm2. Then, the MR ratio is collated with the RA. The size of the reproducing head in the track direction is 70 nm, and the size of the reproducing head in the height direction is 70 nm, and the gap length of the reproducing head is 55 nm.
If the reproducing head is employed by means of vertical recording under the biasing voltage of 120 mV, the output of the reproducing head becomes 1.6 mVpp within a lower frequency range and the S/N of the reproducing head becomes high. As shown in FIG. 1, however, the output voltage of the reproducing head is fluctuated randomly with time. In the case that the reproducing head is installed in the HDD, the AGC (Auto Gain Control) of the HDD may not operate if the output of the reproducing head is often fluctuated at a range of 10%. In this point of view, it is required that the standard deviation in output fluctuation of the reproducing head is reduced within a range of 5% or less.